Also produced and sold by Endress+Hauser are measuring devices under the marks MICROPILOT and PROSONIC, which work according to the travel-time, measuring method and serve to determine and/or to monitor fill level of a medium in a container. In the travel-time, measuring method, for example, ultrasonic waves are transmitted via a sound transducer, or microwaves, or radar waves, are transmitted via an antenna and echo waves reflected on the surface of the medium are received back after a distance dependent travel time of the signal. From the travel time with the assistance of known propagation velocity, the fill level of the medium in a container can be calculated. The echo curve represents, in such case, the received signal amplitude as a function of time, or travel distance, wherein each measured value of the echo curve corresponds to the amplitude of a measurement signal reflected on a surface at a certain distance away.
Because the measuring method uses the reflection principle, the quality of the measurement signal, or of the echo curve, depends, in the case of measuring devices, which work according to the travel-time, measuring method, strongly on the installed position. For example:                the reflection characteristics of the medium;        structurally related disturbance elements in the radiation lobe of the transmission element;        bulk-good cone formation;        filling apparatuses and stirring mechanisms in the container; and        accretion formation of the medium on the sensor unithave a strong influence on the reliability and availability of measuring devices and on the measured values ascertained by them. The effects of these influencing factors on the measurement signal can be minimized by optimized installation of the sensor unit. In the case of the travel-time, measuring method (also called the “time of flight” measuring method), such as e.g. freely radiating microwave, measurements technology and ultrasound, measurements technology, it is important for optimal measuring performance to optimize the measuring situation with the assistance of the installed position of the antenna, respectively, the installed position of the sound transducer.        
In today's state of the art, for optimal orienting of the antenna, or of the sound transducer, operating personnel must step-wise change the position of the sensor unit and observe a characteristic variable appearing on a display (e.g. intensity of the amplitude of the fill-level echo in dB) for the respectively set antenna, or sound transducer, position, in order to be able to evaluate the measuring situation in the container, e.g. a tank. However, the known characteristic variable provides no comprehensive information concerning the orientation, or installed situation, of an antenna, or of a sound transducer, in a container. Most often, only the intensity of the amplitude of the fill-level echo can be taken into consideration.
Furthermore, it is, in today's state of the art, possible to represent the echo function as a function of time on the display of the measuring device or on a networked service tool, and, thus, to ascertain the current measuring situation for the current position of the sensor unit. Such an apparatus for visualizing an echo curve or historical data on a display unit is known from German published patent application DE 100 52 836 A1. The disadvantage of this apparatus is that it is not possible to compare the measuring signals visually with one another for different installation situations of the measuring device and the representation is very slow due to the large amounts of data.
An apparatus for modifying the installed position using a mechanical orienting apparatus of a fill-level measuring device is known from German published patent application DE 101 06 176 A1. Furthermore, an apparatus for changing the radiation characteristic of a planar antenna is known from German published patent application DE 101 49 851 A1. An apparatus for detecting a defective, installed situation of a flow measuring device in a measurement structure is known from German published patent application DE 102 30 607 A1. In this published application (Offenlegungsschrift), an apparatus is presented, which detects a defective installed situation of a vortex, flow measuring system and sends a corresponding error report to a control system. The disadvantage of these examples of an orienting apparatus is that operating personnel need a large amount of technical knowledge, or know how, in order to adjust or orient the measuring device.
Furthermore, the assignee produces and sells measuring devices under the marks LIQUIPHANT AND SOLIPHANT, which follow the limit-level of a medium in a container by means of change of vibratory behavior of an oscillatory element, especially an oscillatory fork.
Known in the state of the art for determining limit level, respectively fill level, and other process variables of a medium are so called oscillatory forks (e.g. European Patent, EP 0 444 173 B1), single rods (e.g. published international application, WO 2004/094964 A1) or also membrane oscillators as oscillatory elements. Used in the case of the respective measurements is the fact that the parameters of the mechanical oscillations (oscillation amplitude, resonant frequency, phase difference versus frequency) of the oscillatable unit depend on contact with the medium and also on the properties of the medium. Thus, for example, frequency or amplitude of the oscillations decreases, especially when the liquid medium reaches and at least partially covers the oscillatable unit. The liquid medium acts on the oscillating body of the sensor—i.e. e.g. the oscillatory fork, or the single rod, or the membrane—, on the one hand, as mass which is dragged along, so that the oscillation frequency sinks, and, on the other hand, as a mechanical damper, so that the oscillation amplitude decreases. Therefore, from the decrease of the oscillation frequency, or the amplitude, it can be deduced that the medium has reached a fill level dependent on the embodiment and the position of mounting of the apparatus. Furthermore, the oscillation frequency is also dependent, for example, on the viscosity of the medium (see e.g. European Patent EP 1 325 301).
For exciting the respective mechanically oscillatable units, piezoelectric elements are often used, which, conversely, also convert the mechanical oscillations into electrical signals. Furthermore, for certain applications, also an electromagnetic excitation of the oscillatable unit is possible.
In the state of the art, there are approaches for designing the sensor units to self-monitoring, i.e. for testing whether the sensor, or individual components of the sensor, is/are capable of working properly. A problem, in such case, is that especially the functional ability of the oscillatable unit, i.e. the component, which comes in contact with the medium and, thus, is exposed to the largest loadings, is not checked in the known measuring methods. However, for exact measuring, it is necessary to assure the installed position of the sensor unit.